This invention relates to low cost fastening systems having fasteners that are easy and quick to install and simple to remove.
There are a myriad of fastening systems presently available to meet a great variety of different applications. Many of these systems use a molded tubular plastic fastener and receptacle in which the fastener is pushed or driven into the receptacle and is secured in the receptacle by friction. Removal is accomplished by pulling the fastener out of the receptacle. The fasteners are often referred to as "pine tree" or "Christmas tree" devices and include a circular head and a cylndrical shank having a plurality of thin, circular fins or ribs. The fins are deformed when the fastener is pushed into a receptacle that has an opening or orifice diameter that is less than the diameter of the ribs. The "memory" of the fastener material provides the frictional force that holds it securely in place in the receptacle. Such fasteners are often difficult to remove without damage, either to the fastener or to the components that are being held.
The fastener of the invention comprises, in its preferred embodiment, a molded plastic screw in which the screw thread is divided into a plurality of thread segments. The segmented construction imparts a degree of flexibility that enables the fastener to be pushed into a lesser diameter tubular receptacle without significant permanent distortion of the thread. The receptacle of the invention includes a single internal thread formed near its entry. The thread engages the thread segments when the fastener is turned into a counterclockwise direction and imparts a longitudinal removal force to the fastener. Thus with the invention, the fastener is driven or pushed into the receptacle by deflecting the resilient thread segments. When the thread segments pass through the one thread entry in the receptacle, they attempt to return to their undeflected positions and, in so doing, exert significant holding forces against the inner surface of the receptacle.